xsd-fu: Issue a warning if genshi is not available

It's a bit more informative than an exception.
Merge pull request #524 from rleigh-dundee/genshi-diag

xsd-fu: Issue a warning if genshi is not available
cpp: replace usage of removed MetadataTools methods

This fixes compile errors introduced by 6b31a4ff9ac4bfc1ccf356804add10dc637366f5
Merge pull request #525 from melissalinkert/cpp-compile-fix

cpp: replace usage of removed MetadataTools methods